001 /*
002 * Copyright 2001-2005 Stephen Colebourne
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016 package org.joda.time;
017
018 /**
019 * Defines a time period specified in terms of individual duration fields
020 * such as years and days.
021 * <p>
022 * The implementation of this interface may be mutable or immutable. This
023 * interface only gives access to retrieve data, never to change it.
024 * <p>
025 * Periods are split up into multiple fields, for example days and seconds.
026 * Implementations are not required to evenly distribute the values across the fields.
027 * The value for each field may be positive or negative.
028 * <p>
029 * When a time period is added to an instant, the effect is to add each field in turn.
030 * For example, a time period could be defined as 3 months, 2 days and -1 hours.
031 * In most circumstances this would be the same as 3 months, 1 day, and 23 hours.
032 * However, when adding across a daylight savings boundary, a day may be 23 or 25 hours long.
033 * Thus, the time period is always added field by field to the datetime.
034 * <p>
035 * Periods are independent of chronology, and can only be treated as durations
036 * when paired with a time via an interval.
037 *
038 * @see ReadableDuration
039 * @see ReadableInterval
040 * @author Brian S O'Neill
041 * @author Stephen Colebourne
042 * @since 1.0
043 */
044 public interface ReadablePeriod {
045
046 /**
047 * Gets the period type that defines which fields are included in the period.
048 *
049 * @return the period type
050 */
051 PeriodType getPeriodType();
052
053 /**
054 * Gets the number of fields that this period supports.
055 *
056 * @return the number of fields supported
057 */
058 int size();
059
060 /**
061 * Gets the field type at the specified index.
062 *
063 * @param index the index to retrieve
064 * @return the field at the specified index
065 * @throws IndexOutOfBoundsException if the index is invalid
066 */
067 DurationFieldType getFieldType(int index);
068
069 /**
070 * Gets the value at the specified index.
071 *
072 * @param index the index to retrieve
073 * @return the value of the field at the specified index
074 * @throws IndexOutOfBoundsException if the index is invalid
075 */
076 int getValue(int index);
077
078 /**
079 * Gets the value of one of the fields.
080 * <p>
081 * If the field type specified is not supported by the period then zero
082 * is returned.
083 *
084 * @param field the field type to query, null returns zero
085 * @return the value of that field, zero if field not supported
086 */
087 int get(DurationFieldType field);
088
089 /**
090 * Checks whether the field type specified is supported by this period.
091 *
092 * @param field the field to check, may be null which returns false
093 * @return true if the field is supported
094 */
095 boolean isSupported(DurationFieldType field);
096
097 //-----------------------------------------------------------------------
098 /**
099 * Get this period as an immutable <code>Period</code> object.
100 * <p>
101 * This will either typecast this instance, or create a new <code>Period</code>.
102 *
103 * @return a Duration using the same field set and values
104 */
105 Period toPeriod();
106
107 /**
108 * Get this object as a <code>MutablePeriod</code>.
109 * <p>
110 * This will always return a new <code>MutablePeriod</code> with the same fields.
111 *
112 * @return a MutablePeriod using the same field set and values
113 */
114 MutablePeriod toMutablePeriod();
115
116 //-----------------------------------------------------------------------
117 /**
118 * Compares this object with the specified object for equality based
119 * on the value and type of each supported field.
120 * All ReadablePeriod instances are accepted.
121 * <p>
122 * Note that a period of 1 day is not equal to a period of 24 hours,
123 * nor is 1 hour equal to 60 minutes. Only periods with the same amount
124 * in each field are equal.
125 * <p>
126 * This is because periods represent an abstracted definition of a time
127 * period (eg. a day may not actually be 24 hours, it might be 23 or 25
128 * at daylight savings boundary).
129 * <p>
130 * To compare the actual duration of two periods, convert both to
131 * {@link Duration}s, an operation that emphasises that the result may
132 * differ according to the date you choose.
133 *
134 * @param readablePeriod a readable period to check against
135 * @return true if all the field values and types are equal, false if
136 * not or the period is null or of an incorrect type
137 */
138 boolean equals(Object readablePeriod);
139
140 /**
141 * Gets a hash code for the period that is compatible with the equals method.
142 * The hashcode is calculated as follows:
143 * <pre>
144 * int total = 17;
145 * for (int i = 0; i < fields.length; i++) {
146 * total = 27 * total + getValue(i);
147 * total = 27 * total + getFieldType(i).hashCode();
148 * }
149 * return total;
150 * </pre>
151 *
152 * @return a hash code
153 */
154 int hashCode();
155
156 //-----------------------------------------------------------------------
157 /**
158 * Gets the value as a String in the style of the ISO8601 duration format.
159 * Technically, the output can breach the ISO specification as weeks may be included.
160 * <p>
161 * For example, "PT6H3M5S" represents 6 hours, 3 minutes, 5 seconds.
162 *
163 * @return the value as an ISO8601 style string
164 */
165 String toString();
166
167 }